1. Field of Invention
The invention relates to a hollow fiber filter for obtaining plasma or plasma water.
2. General Background
Known plasma filters comprise a housing which includes a blood inlet and a blood outlet and an interior. In the interior of the filter housing, a filter membrane is arranged in the form of a plurality of hollow fibers which extend in the longitudinal direction of the housing. The hollow fibers act as capillaries in the filter. The inter-fiber space within the interior forms a "free flow" space in the housing. Blood flows through the hollow fibers and filtrate is drawn through the free flow space. The filtering is effected by pores in the walls of the hollow fibers and by a pressure gradient between the hollow fiber interior and the free flow space which can be produced, for example, by connecting a pump to the free flow space to introduce a transmembrane pressure gradient.
The known filters further comprise a plasma outlet which is in flow communication with the free flow space. The end faces of the hollow fibers are provided with closure members which are usually formed as sealing or casting compound regions and separate the blood inlet and outlet from the plasma outlet. The casting compound regions completely seal both the intermediate spaces between the fibers and the space between the fibers and the housing.
One disadvantage is that a high blood flow resistance opposes the blood flow in the interior of the capillaries and greatly restricts the blood flow. Consequently, a bypass is required with a relatively large blood flow. The bypass requires division of the blood flow into two flows, the amounts being determined by the pressure differences. Also, the filtrate space volume, or the free flow space outside the capillaries, is relatively large. Therefore, taking samples of plasma involves a considerable time delay known as "dead time", associated with filling the filtrate space volume.